Electrolytic method for production of refractory metals



June 8, 1965 M. L. FREEDMAN Filed March 6. 1961 -Fi ci l.

Poms/UM PIA/mum \w HUGE/DE 2 Sheets-Sheet 1 lnven tov: Meger' L'FT-eedman by 0M HIS A=t=t has June 8, 1965 M. FREEDMAN 3,188,282

ELECTROLYTIC METHOD FOR PRODUCTION OF REFRACTORY METALS Filed March 6. 1961 2 Sheets-Sheet 2 lnveni'ov Negev L. F eedman 10 am if 8 His A ttneg United States Patent f 3,188,282 ELECTRQLYTEC METHQD FUR PEQ'DUCTHQN 9F REFRACTGRY METALS Meyer L. Freedman, tlleveland Heights, Gilli), assignor to General Electric Company, a corporation of New York Filed Mar. 6. 1961, Ser. No. 93,471 3'Clairns. (Cl. 204-64) The present invention relates to the electrolytic production of refractory metals.

Refractory metals produced by electrolysis of their compounds in molten salt solutions are of high purity and of coarsely crystalline form. The high purity of refractory metals produced in this manner is particularly desirable for refractory metals which cannot be readily purified after reduction. Metals of this kind include Zirconium, titanium, boron, silicon and beryllium. \Vhile tungsten, tantalum, molybdenum and columbium are -mo re readily purified after reduction, for example by from the disadvantage that the fine powders tend to retain surface impurities to an extent such that the metal so produced is not useful in the industrial arts.

Two solutions of this problem have been proposed.

One proposal is a process involving high temperature reduction including the enclosure of the reactants in a bomb, or by the use of regenerative heat exchange to produce a temperature in the reaction zone which exceeds the sintering temperature of the metal. By this process a sponge rather than a powder of metal is produced which is more readily adaptable to industrial use. However, difficulty is experienced in removing undesired salts adhcrin to the metal so produced.

The other proposal is a process which includes the electrolysis of molten salts. In this method sodium is generated at -a controlled rate by electrolysis ,of the mixed molten salts and liberates the desired metal by secondary reaction. Dtfficulties are encountered due to reactions at the solid anodes used and to problems of cell construction. Massive metal is frequently obtained, but production costs are such that this method is not generally competitive.

The principal object of the present invention is to rovide a method and an apparatus for the production of refractory metal by electrolysis of a metal compound in a bath of molten salt which avoids the difficulties encountered heretofore while retaining the desirable high purity and massive crystalline form characteristic of metal produced in this manner. vantages of the invention will be apparent to those skilled in the art from the following description and the accompanying drawings.

The invention attains its objects by utilizing an electric current generated by chemical reaction in a fused salt electrolytic cell for reducing at the cathode of the cell a compound of the metal to be produced. In accordance with the invention, the chemical reactants are separated rather than mixed with each other in the molten salt bath with the reductant at the anode and the reducible metal compound or oxidant at the cathode. The anode and the cathode of the cell are connected together Other objects and ad- 3,l88,282 Patented June 8, 1955 by a conductor of electrons and means is provided in the cell to restrict atomic diffusion of'the reactants in the fused salt bath While permitting ionic transport or migration. The reductant for the metal compound to be reduced is liquid at the temperature at which the salt bath is molten and constitutes the soluble anode of the cell. The cell embodying the invention completely avoids the tficulties encountered heretofore in prior electrolytic cells using solid anodes while retaining the advantageous feature of such cells in producing metal of high purity and coarsely crystal-line form.

Further, the cell of the present invention generating by chemical reaction the electric current necessary for reducing the metal compound elhninates the need for separate sources of current used heretofore to substantially reduce the cost of the apparatus required while producing superior results. The efficacy of the cell of the present invention incorporating the features of a primary or voltaic cell is unexpected and as far as applicant is aware has not been appreciated heretofore by prior investigators who have used external sources of current for effecting electrolysis of metal compounds in molten salt solutions.

In the drawings accompanying and forming part of this specification electrolytic cells embodying the invention and useful in carrying out the method of the invention are shown by way of example in which,

FIG. 1 is a schematic representation of one form of electrolyti cell embodying the invention;

FIG. 2 is a similar View of another electrolytic cell of slightly different structure and also embodying the invention.

FIG. 3 is a similar view of another electrolytic cell of slightly different structure and also embodying the I comprises a nickel crucible l to hold the molten salts.

A crucible having a capacity of 100 cubic centimeters was used in carrying out the process. in assembling the cell 10 grams of potassium tantalum fluoride (KzTaFq) was used as the reducible metal compound, was placed in the bottom of the crucible 1 and was covered-with 20 grams of sodium chloride-potassium chloride mixture. The circular screen 2 of 1 /2 inch diameter was then press fitted into place in the crucible l. A lb-mesh screen of Mouel metal was used.

A nickel crucible 3 of cubic centimeter capacity was used to hold the reductant, in this case sodium. The bottom of crucible 3 was supported partially immersed in the salt bath w on the salt mixture was in a molten condition by the nickel triangle 4 engaging both crucibles 1 and 3. The crucible 3 was provided with a mesh Monel metal screen 5 covering the circular opening in the bottom thereof. The bottom opening in the crucible 3 was 4 inch. In assembling the cell the crucible 3 was closed at the bottom by a preliminary fusion of grams of the sodium chloride potassium chloride mixture in the crucible I placed above the screen 2. The crucible 3 sank into the position shown in FIG. 1 while the salt mixture was molten.

A sodium filter 6 was used to free the sodium from oxide before the molten sodium entered the crucible 3. The filter 6 consisted of a 75 cubic centimeter nickel crucible 7 similar to the crucible 3 and had a 60-mesh screen 8 of Monel metal across and covering its open bottom. It rested on the crucible 3 with its bottom above that of the crucible 3, as shown.

Ten grams of solid sodium was placed in the crucible of sodium chloride and potassium chloride.

was perforated and the crucible 3 The assembled cell was placed in the bottom of the elongated ceramic tube 9 which was closed at the bottom and open at the top. The tube 9 was a vitreous silica tube, known commercially as a Vitreosil tube, and was 3 /2 inches in diameter.

The tube 9 with the cell in place was purged with an inert gas, argon, before the part thereof containing the cell was lowered into the furnace. A slight pressure of the inert gas was maintained in the tube 9 while the cell was in the furnace and while it was cooling after removal from the furnace. A vitreous conduit 10 extended through the resilient stopper 11 of soft rubber, for example, for this purpose. The stopper 11 closed the open end of the tube 9 except for the passage through the conduit 10 through which the interior of the tube 9 was first evacuated and then filled with argon repeatedly until the apparatus was purged of air and other undesired gaseous material.

The outer end of conduit 10 was connected to the usual vacuum system and gas supply system (not shown) the latter being adapted to fill the tube 9 with argon at a pressure slightly higher than atmospheric pressure while the lower end of the tube 9 containing the electrolytic cell was in the furnace 12. A heat reflector disc 13 of nickel was mounted on the end portion of conduit is to protect the rubber stopper 11. from excessive temperatures.

The furnace 12, which was of the electrically heated type, was heated to and maintained at a temperature sufliciently elevated to melt the salt bath without caus ing excessive volatilization of either the sodium or the potassium tantalum fluoride. The bath temperature was approximately 800 C.

At the conclusion of each run the tube was lifted out of the furnace and the solidified salts were broken out of the crucible 1 after cooling under argon. The salts were placed in water which was boiled to extract the soluble salts. The residue was boiled with a hydrochloric acid solution and colloidal metal washed away with distilled water. The remaining metal was then rinsed in acetone and air dried.

The above procedure was repeated four times and massive tantalum metal was obtained each time. The product yield varied from about 10 to 80% depending on the length of the run, from minutes to 4 hours, and consisted of large flakes and crystals of tantalum metal containing less than 0.01% of copper, iron or nickel as impurities. The metal flakes were soft, ductile and easily compacted by conventional metallurgical meth ods into mechanically strong pellets. The large flakes and crystals of the tantalum metal were found adhering to the diaphragm 2 and to the wall of crucible 1 beneath the unreacted tantalum salts.

In a fifth repetition of the above procedure tantalum metal were produced which contained plates with bright, well formed crystalline faces. The temperature during this run was below 800 C. and was about 750 C.

It is apparent from the foregoing that the reduction of the potassium tantalum fluoride salt to the metal tantalum took place in the cathode region of the cell, the cathode being constituted by the nickel crucible 1 and the Monel metal screen 2. None of the tantalum metal was found at the end of any of the runs in the anode region of the cell, the anode being constituted by the liquid sodium and the nickel crucible 3.

The screens 2 and 5 thus were effective in preventing atomic or molecular diffusion or convection of the liquid sodium or the potassium tantalum fluoride salt in the bath. Since the latter salt was effectively reduced to tantalum metal in the cathode region of the cell it is apparent that the cell constructed in the above-described manner functioned as a voltaie cell in which the metallic conductor was constituted by the crucible 3, the triangle 4 and the crucible 1 for the passage of electrons from the reductant constituted by the liquid sodium to the 4 oxidant constituted by the potassium tantalum fluoride. It is apparent further that the diffusion of ions occurred in the salt bath to cause the flow of electrons in the metallic conductor.

This phenomenon was investigated further in the cell illustrated in FIGURE 2 of the drawings and incorporated herein as another example of the invention.

The cell illustrated in FIG. 2 includes a cylindrical container 13 ten centimeters in diameter and consisting of stainless steel. The container 13 is provided with an outwardly extending annular flange 14 also of stainless steel and having its inner periphery beveled as shown in the drawing. The inner periphery or rim of the annular flange 14 makes a mechanical fluid tight joint with the matching outer rim of the flange 15, also of stainless steel, provided on the lower end of the stainless steel cooling chamber 16 of the cell.

A cooling coil 17 is mounted on the upper end of the cooling chamber 16 which is connected to a conventional cooling apparatus (not shown). The interior of the cylindrical container 13 is provided with a baffle 18 of sheet nickel which is supported by short legs of nickel wire resting on the bottom of the cell 13. As shown in FIG. 2 of the drawing the baflle is supported in a raised position by the legs 19 to provide a passage 20 in the nature of a circular slit between the annular space surrounding the baflle and the circular space within the battle. The upper end of the baffle is flanged and the outwardly flaring flange 21 rests against the side wall of the cell to center the battle and is provided with an opening 22 beneath the sodium port 23 provided in the flange 15 on the cooling chamber 16 as shown in the drawing. The flange 15 is also provided with an argon inlet 24 connected to a source (not shown) of argon under pressure slightly greater than atmospheric pressure.

The cathode assembly 25 is made up of a 5 centimeter diameter nickel tube 26 provided with two rows of closely spaced openings 0.6 centimeter in diameter and arranged in alternation. The nickel tube 25 is secured to the flange provided at the end of the nickel conduit 28 which at its opposite end is provided with a nickel heat shield 29 and a soft rubber stopper 30 for closing the opening at the upper end thereof during operation of the apparatus.

A similar rubber stopper 31 is provided to close the annular opening between the cooling chamber 16 and the conduit 28. The lower perforated portion of the nickel tube 26 is covered by a nickel diaphragm 32 which is Wired onto the tube 26 by nickel wires and folded over the bottom of the tube 26 to support the sheet nickel bottom plate 33 on the tube 26. r

The diaphragm 32 is made up of a 40-mesh Monel metal screen with a paste of nickel powder filling the openings therein. The screen provided with the nickel powder is first dried and then sintered in hydrogen at 1100 C. for porosity. Bottom plate 33 of the cathode assembly is supported in a slightly raised position with respect to the bottom of the container 13 by the rubber stopper 31 inserted in the opening of cooling chamber 16 and frictionally engaging around the conduit 28.

The container 13 is supported in a lifted position w1th respect to the bottom of the furnace 34 by the flange 14 resting on the upper rim of the furnace 34.

The furnace 34 is of the pot type and was provided with electrical heating elements at both the side and bottom.

Before each run the cell is vacuum dried with the cathode 25 lifted into the cooling chamber 16 and the salt charge contained in the bottom of the container 13. A steel cover having connections to vacuum and argon and a rubber gasket (not shown) located over the cooling chamber 16 and the conduit 28 of the cathode and resting on the flange 14 of the container 13 is used during vacuum drying.

To show the effectiveness of the cell in reducing metal compounds to metals the following example is given.

A charge of 650 grams of equimolar chemically pure sodium chloride and potassium chloride was placed in the bottom of the container 13 to provide a layer of salt which was molten at 750 C., and provided a liquid bath of 6 cm. depth. During the melting of the salt access of air into the cell was prevented by a stream of argonfiowing through the argon inlet 24 at a pressure slightly above atmospheric. The flow of argon was continued during the entire run. After melting the salt bath the cathode 25 was lowered to the bottom of the container 13 and sodium metal was added to the continer through the sodium port 23 after the sodium metal had been melted through a porous stainless steel filter to remove oxides. Five grams of vacuum dried technical grade K ZrF was then introduced into the space defined by the lower end of the cathode, hereinafter called the cathode chamber. Additional quantities were added at minute intervals during the course of the run, each additional quantity being introduced to the cathode chamber through the conduit 28. During the run the electrically conducting metal wire 34 was connected to the flange 14 and the conduit 28. At the conclusion of a run the cathode was raised slowly to permit drainage of molten salt and then cooled under argon in the upper chamber. The cathode after cooling was then dismantled and the zirconium crystals separated from adhering salts by boiling first with water and then with dilute hydrochloric acid solution.

With the cell constructed as described above and when grams of K ZrF was added over a four-hour period, 11.5 grams of washed zirconium crystals were obtained for a yield of 89%. The addition of 40 grams of K ZrF in three hours reduced the yield at the cathode to 80% of theoretical. The metal was deposited as a thick pad of dendritic crystals over the interior walls and the bottom of the cathode. This permitted the drainage of molten salts so that a weight of salt equal to only about twice of that of the zirconium was retained by the cathode. The recovered metal powder was of a silvery gray color with a bulk density of 0.9 g./ cc.

A 100 mesh screen retained'approximately so the average particle size was estimated as 150 micron. A qualitative spectrochemical analysis indicated only traces of iron and nickel impurities. While the particle size is similar to that reported for electrolytic zirconium the dendritic form is more pronounced. Compaction to 80% of theoretical density was obtained on pressing at 50 tons/in. The sample thus compares favorably in this respect to hydride zirconium powders. A Rockwell B hardness of 90 was determined on a pellet which had been further consolidated by electron beam melting. This value is well within the range for commercially pure zirconium.

The design of this cell did not permit successful re-use of the salt charge. The zirconium obtained in the second run with the same salt bath was a mixture of dendritic crystals and fine black powder similar to the powder obtained by direct reduction of K ZrF with sodium. During the time required for the removal of one cathode and the insertion of a second, atomic sodium had apparently difiused into the bulk of the molten salt. This then reacted directly with the K ZrF as it was added to the new cathode. For continuoususe of the salt bath, provision must thus be made for sealing off the sodium compartment between runs. Otherwise, a second porous diaphragm might be used to restrict the atomic diflusion of sodium while permitting ionic transport.

The anode slit height, fixed by the distance between the bottom of the battle and the cell bottom, was also found to greatly infiuencethe character of the extracted zirconium. A slit heightof approximately 2 millimeters was generally used. A voltmeter connected in place of the ground wire then registered 0.6 volt with the cathode raised slightly above the cell bottom during a run. When the anode slit height was increased to 5 millimeters the volt meter registered nearly zero. Zirconium was still deposited on the interiorsurface of the cathode in good yield. However, instead of dendritic crystals, the metal now consisted of irregular gray flakes having rough pebbled surfaces. The zirconium in this form prevented the drainage of molten salt from the cathode at the end of the run and was also difiicui to wash free of salt. ,With the enlarged anode slit the concentration of atomic sodium in the molten salt adjacent to the cathode must have been nearly as high as the concentration within the sodium cornpartment. Under these conditions, the outer surface of the cathode itself would serve as the anode. I While fluoride salts were used in these procedures, the voltaic cell process should be more advantageous with a chloride feed. In the absence of fluorides, a porous ceramic diaphragm could be used to enclose the cathode volume while a porous metallic diaphragm would confine the sodium. Continuous operation could then be obtained with .solid cathodes and molten NaCl.

The cell illustrated in FIG. 3 of the drawing is slightly simplified in structurethough including the same essential elements of the cells shown in FIGS. 1 and 2.

In this embodiment of the invention the container 36 is a stainless steel pot provided with an air tight cover 37 also of stainless steel and having a central opening in which a bushing '38 is provided. The bushing 38 permits the raising and lowering of the cathode assembly 39 in the cell as while making a gas tight connection with the conduit 49 of the cathode assembly. The container 35 is provided with a port 41 connected to a vacuum or an argon supply system (not shown) and another port 42 through which metallic sodium is introduced into the interior of the container 36 as described in the previous embodiments. The batiie 43 corresponding to-the baffle 18 in the embodiment shown in PEG. 2 is also of sheet nickel and is provided at its lower end with a Monel metal screen filled with nickel and made porous by the drying and sintering in hydrogen procedure described in connection with the cathode diaphragm 32 of the embodiment of PEG. 2. The screen, which is shown at 44, in the'drawing constitutes a porous nickel anode diaphragm of the cell. The baffle constituted by the members 43 and 44' rests upon the bottom of the container 36 to divide the container into compartments as mentioned in connection with the embodiment of FIG. 2.

The cathode assembly 3? of the cell is similar to the cathode assembly 25 of the cell shown in FIG. 2 in that it comprises the conduit 4t through which the salt of the metal be extracted or reduced is introduced into the space within the lower part of the cathode. The lower part of the cathode is made up of a cylindrical bell or cup-shaped member 45' of sheet nickel to which is fastened the cathode diaphragm 46 which consists of porous nickel. The bottom of the cathode is constituted by a nickel disc which is'attached to the diaphragm 46 and which rests upon the bottom of the cell 36 in the lowered position of the cathode assembly 39. An opening 4-3 is provided at the top of the cathode for access to the atmosphere within the cell when the cathode assembly is in its lowered position' For purposes of assuring an adequate supply of argon or other inert gas to the interior of the cathode bell during operation of the cell a port 49 is provided at thepart of the conduit 6 external to the container 36 both in the lowered and lifted position of the cathode assembly 39. As in the embodiment ofFIG. 2 an electrically conducting metal wire 50 is connected to the cover 37 of the'container 35 and to the conduit 4%) of the cathode assembly 3% during the entire run or" the cell.

As an illustration of the effectiveness of the cell in reducing compounds of refractory metals to metal the following is given byway of example.

The cell was assembled with the cathode assembly lifted in the container 36 so that the cathode bell was out of the furnace '51 and at the top of the container 36 and a charge of 800 grams of mixed sodium and potassium chloride was melted under argon after vacuum drying of the cell to give a 2" layer of molten salt at the bottom of the container 36. The cathode assembly 39 was then lowered to the position shown in FIG. 3 and sodium metal freed from its oxides as described above was added to the port 42. The sodium metal floats on the top of the molten salt in the annular space between the bafiie 43 and the cylindrical wall of the container 36. The metal salt was then added periodically through the conduit iil to maintain the desired concentration of the metal salt in the molten salt in the cathode chamber or compartment. The total quantity of the metal salt to be reduced is slightly less than that required to react with the weight of the metal sodium. At the conclusion of the run when the concentration of metal salt in the cathode compartment reached a low value, the cathode was raised out of the molten salt and the cell removed from the furnace 51 and allowed to cool. The cathode was then removed from the container 36 and the metal powder extracted from the reducible metal compound recovered. from the inner cathode diaphragm surface by dissolving away residual salts. The cooled cell was kept filled with argon to prevent oxidation of the excess sodium between runs.

In one of the runs following the above procedure the mixed sodium and potassium chloride salts were melted at 750 C. and 30 grams of sodium were added to the anode compartment, then 90 grams of vacuum dried K ZrF were added to the cathode compartment over a four-hour period, grams being added every 30 minutes. A sample of molten salt taken from the cathode compartment contained 1.67% K ZrF at the end of four hours. The reaction was allowed to proceed an additional hour when a sample of the salt was found to contain only 0.11% K ZrF. The cathode was then raised, one-half inch every 10 minutes, to drain the molten salt and the cell was then cooled to room temperature. A porous pad of zirconium metal and the residual salt on the interior wall of the cathode was leached with water to recover 27 grams of dendritic zirconium crystals, a yield of 93%.

In another run utilizing the cell of FIG. 3 and the procedure described above, 40 grams of sodium metal were introduced into the cell and 120 grams of K' ZrF were added at the rate of 40 grams per hour. At the end of 3 hours the concentration of K ZrF in the cathode compartment was found to be 8.8%. The run was continued for an additional hour and the cathode then removed as described above. A recovery of 35.5 grams of zirconium was obtained for a yield of 92%. However, the metal powder was found to be less dendritic than previously and consisted of blocky crystals similar to that obtained by fused salt electrolysis at high K ZrF concentrations.

In another run utilizing the apparatus shown in FIG. 3 the anode diaphragm :4 was removed and the bathe 4-3 supported on legs of nickel wire with its bottom raised about above the bottom of the container 36. This provided an anode slit of a corresponding height between the bottom of the cell and the bafiie. Seventy-five grams of sodium was added to the fused salt bath and 230 grams of K ZrF were added to the cathode compartment as described above over a 5 /2 hour period. Also the cathode diaphragm 46 was 24 square inches in this case.

At the end of the run the K ZrF concentration was found to be 2.78% at the time the last addition was made. The cathode deposit contained fine grain. zirconium powder which was separated by washing as above described to leave 54 grams of coarse powder, a 75% recovery.

In another run utilizing the apparatus shown in FIG. 2 with the nickel baffle replaced by an iron tube supported /s above the bottom of the cell the compound KgHfFe was reduced with magnesium. In this run 20 grams of magnesium metal turnings were placed in the anode compartment, the salt was melted at 750 C. and the cathode which had a diaphragm of 0.9 square inch in area was lowered to the cell bottom, that is to the bottom of the container 13. Thirty grams of K HfF were added to the cathode over a three-hour period and 7 /2 grams of hafnium metal powder was recovered from the inside of the cathode.

Using the same apparatus of FIG. 2 as modified as described above in connection with the reduction of K i-HR, with magnesium the compound K MoCl was reduced with zinc. Since the zinc metal is more dense than the molten salt and sinks to the bottom of the salt bath the bafile 13 was omitted. Twenty grams of zinc shot were added to the salt bath in the manner described in connection with the addition of sodium in the embodiment of FIG. 2. The cathode was lowered nearly to the bottom of the container 13 and 40 grams of K MoCl were added over a four-hour period. The recovery was 7.5 grams of coarse molybdenum metal from inside the cathode.

I Columbium metal was produced utilizing the apparatus shown in FIG. 2 of the drawings except that the bottom plate of the cathode consisted of tantalum and the nickel bathe was replaced by a 2.5 inch diameter steel tube with a inch rim of porous stainless steel welded to the bottom of the baffie. The cathode diaphragm was of 60 mesh Monel metal cloth filled with porous nickel and provided an effective area of 0.9 square inch. A salt charge of 650 grams was used as in the runs described above in connection with FIG. 2. K CbI- of technical grade was used without purification. A molten anode of sodium metal was used. The K CbF was added at the rate of 10 grams per hour and these additions were made once an hour for the first run and at 30-minute intervals for two other runs. Columbium was produced in platelet form on each of the three runs. Molten salts drain freely from the cathode deposits and these deposits were then leached with water and dilute hydrochloric acid. The recovery from the cathode and the bottom of the container was such that the yield obtained was approximately The separate lots of columbium metal powder obtained from the runs were combined and compacted and densified in the conventional manner and the densified pellet had a Rockwell B hardness of 68.

It will be understood that in the runs described above by way'of example and utilizing the apparatus shown in FIGS. 2 and 3 of the drawings, the temperature of the molten salt bath during each of the runs was approximately 750 C. and that, unless otherwise noted, the procedures followed in each of the runs was that described in con nection with the first example given in connection with each of these figures.

What I claim as'new and desire to secure by Letters Patent of the United States is:

1. In the method of producing refractory metal by electrolytic reduction of a compound of the metal dissolved in molten salt inert to said refractory metal under an inert atmosphere contained in an electrolytic cell having a soluble metal anode, the steps comprising introducing into the cell as the soluble anode a reductant for the metal compound, which reductant is liquid at a temperature at which the salt is molten, introducing at the cathode of the cell as the oxidant the metal compound to be reduced and positioning between the reductant and the oxidant means for restricting the diffusion of the reductan-t and the oxidant in the molten salt to the difilusion of ions only, connecting together the anode and the cathode of the cell by a conductor of electrons and heating the cell to a temperature and for a time sufiicient to cause the anode to dissolve and electrons to flow in the electron conductor from the anode to the cathode of the cell to reduce the metal compound to metal.

2. In the method of producing refractory metal by electrolytic reduction of a compound of the metal in molten fused salt inert to said refractory metal under an inert atmosphere contained in an electrolytic cell having a soluble metal anode, the steps comprising introducing into the cell as the soluble anode a reductant for the metal compound, which reductant is liquid at a temperature at which the salt is molten, introducing at the cathode of the cell as the oxidant the metal compound to be reduced and positioning between the reductant and the oxidant means for restricting the diffusion of the reductant and the oxidant in the molten salt to the diifusion of ions only and at relative rates such that the reduction of the metal compound occurs principally at the cathode during electrolysis, connecting together the anode and cathode of the cell by a conductor of electrons and heating the cell to a temperature and for a time sufiicient to cause the anode to dissolve and electrons to flow in the electron conductor from the anode to the cathode of the cell to reduce the metal compound to metal at the cathode.

3. In the method of producing refractory metal of the group consisting of tantalum, zirconium, hafnium, molybdenum and columbium by electrolytic reduction of a compound of the metal dissolved in molten salt inert to said refractory metal under an inert atmosphere contained in an electrolytic cell having a soluble metal anode, the steps comprising introducing into the cell as the soluble anode a reductant for the metal compound, which reductant is 25 10 difiusion of ions only, connecting together the anode and the cathode of the cell by a conductor of electrons and-heating the cell to a temperature and for a time sufficient to cause the anode to dissolve and electrons to flow in the electron conductor from the anode to the cathode of the cell to reduce the metal compound to metal.

References Cited by the Examiner UNITED STATES PATENTS 1,336,281 4/20 Cataldi 204-248 1,861,625 6/32 Driggs et al. 204-64 2,713,554 7/55 Pitzer 204-248 2,900,318 8/59 Andrews 204-246 2,904,491 9/59 Moles 204-246 2,913,378 11/59 Dean et al. 204-246 2,956,936 10/60 Huber 204-64 2,985,569 5/61 Gendvil 204-246 3,019,174 1/ 62 Brenner et al. 204-64 FOREIGN PATENTS 23,557 11/95 Great Britain. of 1894 OTHER REFERENCES Status Report on Fuel Cells, Stein, Aro Report No. 1 (June 1959), pages 21-26.

WINSTON A. DOUGLAS, Primary Examiner.

JOHN R. SPECK, JOHN H. MACK, Examiners. 

1. IN THE METHOD OF PRODUCING REFRACTORY METAL BY ELECTROLYTIC REDUCTION OF A COMPOUND OF THE METAL DISSOLVED IN MOLTEN SALT INERT TO SAID REFRACTORY METAL UNDER AN INERT ATMOSPHERE CONTAINED IN AN ELECTROLYTIC CELL HAVING A SOLUBLE METAL ANODE, THE STEPS COMPRISING INTRODUCING INTO THE CELL AS THE SOLUBLE ANODE A REDUCTANT FOR THE METAL COMPOUND, WHICH REDUCTANT IS LIQUID AT A TEMPERATURE AT WHICH THE SALT IS MOLTEN, INTRODUCING AT THE CATHODE OF THE CELL AS THE OXIDANT THE METAL COMPOUND TO BE REDUCED AND POSITIONING BETWEEN THE REDUCTANT AND THE OXIDANT MEANS FOR RESTRICTING THE DIFFUSION OF THE REDUCTANT AND THE OXIDANT IN THE MOLTEN SALT TO THE DIFFUSION OF IONS ONLY, CONNECTING TOGETHER THE ANODE AND THE CATHODE OF THE CELL BY A CONDUCTOR OF ELECTRONS AND HEATING THE CELL TO A TEMPERATURE AND FOR A TIME SUFFICIENT TO CAUSE THE ANODE TO DISSOLVE AND ELECTRONS TO FLOW IN THE ELECTRON CONDUCTOR FROM THE ANODE TO THE CATHODE OF THE CELL TO REDUCE THE METAL COMPOUND TO METAL. 